Solid-state imaging device, method of manufacturing solid-state imaging device, and electronic apparatus

ABSTRACT

A solid-state imaging device including an imaging area where a plurality of unit pixels are disposed to capture a color image, wherein each of the unit pixels includes: a plurality of photoelectric conversion portions; a plurality of transfer gates, each of which is disposed in each of the photoelectric conversion portions to transfer signal charges from the photoelectric conversion portion; and a floating diffusion to which the signal charges are transferred from the plurality of the photoelectric conversion portions by the plurality of the transfer gates, wherein the plurality of the photoelectric conversion portions receive light of the same color to generate the signal charges, and wherein the signal charges transferred from the plurality of the photoelectric conversion portions to the floating diffusion are added to be output as an electrical signal.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.14/495,318 filed Sep. 24, 2014, which is a continuation of U.S. patentapplication Ser. No. 13/085,676 filed Apr. 13, 2011, the entireties ofwhich are incorporated herein by reference to the extent permitted bylaw. The present application claims the benefit of priority to JapanesePatent Application No. JP 2010-107265 filed on May 7, 2010 in the JapanPatent Office, the entirety of which is incorporated by reference hereinto the extent permitted by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a solid-state imaging device, a method ofmanufacturing the solid-state imaging device, and an electronicapparatus.

2. Description of the Related Art

An electronic apparatus such as a digital camera includes a solid-stateimaging device. For example, the solid-state imaging device includes aCMOS (Complementary Metal Oxide Semiconductor) type image sensor and aCCD (Charge Coupled Device) type image sensor.

In the solid-state imaging device, an imaging area where a plurality ofunit pixels are arrayed in a matrix shape is disposed in a semiconductorsubstrate. In each of the unit pixels, a photoelectric conversionportion is disposed. The photoelectric conversion portion is, forexample, a photodiode and generates signal charges by receiving incidentlight incident through an externally attached optical system by alight-receiving plane and photoelectrically converting the light.

Among the solid-state imaging devices, in the CMOS type image sensor,the unit pixel is configured so that a plurality of transistors areincluded in addition to the photoelectric conversion portion. Theplurality of the transistors are configured to read out the signalcharges generated in the photoelectric conversion portion and to outputan electrical signal to a signal line. For example, four transistors,that is, a transfer transistor, a reset transistor, an amplificationtransistor, and a selection transistor are disposed as the pixeltransistors on the front surface of the semiconductor substrate. Inaddition, wire lines of electrically connecting these transistors areprovided in the front surface of the semiconductor substrate.

There is a demand for solid-state imaging device may be desired to havehigh sensitivity. Particularly, in a digital camera used under lowerluminance such as an endoscope camera and a monitoring camera, highsensitivity is necessary.

Therefore, it is considered that the high sensitivity is necessarilyimplemented by expanding an area of the light-receiving plane byincreasing a pixel size.

In addition, there have been proposed technologies in which one set ofpixel transistors is shared by a plurality of photoelectric conversionportions, so that high sensitivity is implemented by increasing an areaoccupied by the light-receiving plane in the unit pixel. For example,one set of the pixel transistors is shared by two or four photoelectricconversion portions (for example, refer to Japanese Unexamined PatentApplication Publication Nos. 2004-172950, 2006-157953, and 2006-54276).

Additionally, there have been proposed techniques in which a microlensfor focusing incident light on a light-receiving plane is disposed toeach unit pixel, so that high sensitivity is implemented (for example,refer to Japanese Patent No. 2600250).

In addition, there have been proposed technologies in which a focusingefficiency is improved by measures such as optimization of the shape ofan in-layer lens, reduction of the number of wire-line layers, orintroduction of an optical waveguide, so that high sensitivity isimplemented (for example, refer to Japanese Unexamined PatentApplication Publication Nos. 2002-314058 and 2003-324189).

SUMMARY OF THE INVENTION

FIG. 18 is a diagram illustrating an array of unit pixels P in a CMOStype image sensor. In FIG. 18, a portion where two unit pixels P in eachof the horizontal direction x and the vertical direction y are alignedto be adjacent to each other is illustrated.

As illustrated in FIG. 18, in each of the four unit pixels P, aphotodiode 21 and a transfer transistor 22 are disposed. In addition,under the four unit pixels P, a transistor group constructed as a set ofan amplification transistor 23, a selection transistor 24, and a resettransistor 25 is disposed. In other words, the four unit pixels Pincluding the photodiode 21 and the transfer transistor 22 areconfigured so as to share the transistor group constructed as a set ofthe amplification transistor 23, the selection transistor 24, and thereset transistor 25.

More specifically, as illustrated in FIG. 18, the two photodiodes 21 arealigned in the vertical direction y. In addition, the transfer gates 22Gof the two transfer transistors 22 are disposed so as to be aligned inthe vertical direction y between the two photodiodes 21 aligned in thevertical direction y. In addition, between the two transfer gates 22Galigned in the vertical direction y, the floating diffusion FD isdisposed.

In addition, as illustrated in FIG. 18, sets constructed with the twophotodiodes 21, the two transfer gates 22G, and the floating diffusionFD aligned in the vertical direction y are disposed so as to be alignedin the horizontal direction x. Although not shown, the floatingdiffusions FD aligned in the horizontal direction x are electricallyconnected to each other, and the floating diffusions FD are connected tothe gate of the amplification transistor 23.

In addition, as illustrated in FIG. 18, in each unit pixel P, themicrolens ML and the color filter CF are disposed, so that the incidentlight incident sequentially through the microlens ML and the colorfilter CF is received by the photodiode 21.

The color filter CF includes a red filter layer CFR, a green filterlayer CFG, and a blue filter layer CFB. The red filter layer CFR, thegreen filter layer CFG, and the blue filter layer CFB are adjacent toeach other, and one thereof is disposed corresponding to each of theunit pixels P.

Herein, as illustrated in FIG. 18, the red filter layer CFR, the greenfilter layer CFG, and the blue filter layer CFB are disposed so as to bealigned in a Bayer array.

FIGS. 19A and 19B are conceptual diagrams illustrating a potential inthe unit pixel P in the CMOS type image sensor. In FIGS. 19A and 19B,the potentials in a portion taken along line XIX-XIX of FIG. 18 areillustrated.

As illustrated in FIG. 19A, in the case where the electric fieldgradient in the photodiode 21 is small, there may be problems in that atransfer time of the signal charges is increased and some signal chargesare not transferred but remain, so that an after image occurs.

Therefore, as illustrated in FIG. 19B, the occurrence of the problem issuppressed by increasing the electric field gradient in the photodiode21 so that the signal charges are moved to the side of the transfertransistor 22. In this case, for example, an ion injection process isadded, so that the photodiode 21 is formed as illustrated in theabove-described potential diagram.

FIGS. 20 and 21 are diagrams illustrating behaviors of incident lightincident on the unit pixel P of the CMOS type image sensor. Herein, FIG.20 illustrates a behavior in the case where the main light beams H21 areincident on upper pixels PU disposed in the upper end portion in theimaging area where a plurality of the unit pixels P are arrayed. Inaddition, FIG. 21 illustrates a behavior in the case where the mainlight beams H22 are incident on lower pixels PL disposed in the lowerend portion in the imaging area where a plurality of the unit pixels Pare arrayed.

As illustrated in FIGS. 20 and 21, the photodiode 21 and the floatingdiffusion FD are disposed in an upper layer portion of the semiconductorsubstrate 101. In addition, the transfer gate 22G constituting thetransfer transistor 22 is disposed through a gate insulating film (notshown) on the surface of the semiconductor substrate 101, on which themain light beams H21 and H22 are incident. The transfer gate 22G isformed with, for example, a conductive light-blocking material such aspolysilicon.

As illustrated in FIGS. 20 and 21, in the upper end portion or the lowerend portion of the imaging area, the main light beams H21 and H22 arenot incident in the direction z perpendicular to the surface of thesemiconductor substrate 101 but they are incident in the directionslanted with respect to the direction z (refer to FIGS. 1 and 2 andrefer to FIG. 3 or the like in Japanese Patent No. 2600250). Herein, ineach unit pixel P, since the main light beams H21 and H22 are incidentthrough color filters, the main light beams H21 and H22 are incident onthe photodiode 21 as colored light such as red light or green light.

Therefore, as illustrated in FIG. 20, in the upper pixel PU located inthe upper end portion of the imaging area, a portion of the green lightamong the main light beams H21 is blocked by the transfer gate 22Gbefore the portion of the green light is incident on the photodiode 21.On the other hand, in the adjacent unit pixel P, the red light among themain light beams H21 is not blocked by the transfer gate 22G before thered light is incident on the photodiode 21. In other words, vignettingof the green light occurs, but vignetting of the red light does notoccur.

On the contrary, as illustrated in FIG. 21, in the lower pixel PLlocated in the lower end portion of the imaging area, a portion of thered light among the main light beams H22 is blocked by the transfer gate22G before the portion of the red light is incident on the photodiode21. On the other hand, in the adjacent unit pixel P, the green lightamong the main light beam H21 is not blocked by the transfer gate 22Gbefore the green light is incident on the photodiode 21. In other words,unlike the upper end portion of the imaging area, in the lower endportion of the imaging area, vignetting of the green light does notoccur, but vignetting of the red light occurs.

In this manner, in the end portion of the imaging area, since vignettingratios are different among the colors, there may be a problem in thatthe color shading occurs, so that the image quality of the color imageis deteriorated.

Particularly, in a small-sized electronic apparatus such as a capsuleendoscope a portable camera, there may be problems in that theconsiderable color shading occurs, so that the image quality of thecolor image is deteriorated. In other words, in the aforementionedsmall-sized electronic apparatus, in many cases, the volume for mountingan externally-attached lens module is necessarily reduced, and thus, themaximum main light beam angle of the lens is configured to be large forthe small thickness of the apparatus, so that the considerable colorshading occurs.

Besides, in the case where the pixel size is increased in order toimprove the sensitivity, there are problems in that, since the distancebetween the center of the photodiode 21 and the transfer transistor 22is increased, the charge transfer efficiency is decreased, so that theafterimage occurs.

In this manner, in some cases, in the solid-state imaging device, it isdifficult to simultaneously obtain prevention of the occurrence of thecolor shading, the afterimage, or the like and improvement of thesensitivity. As a result, it is difficult to improve the image qualityof the captured image.

Therefore, it is desirable to provide a solid-state imaging devicecapable of improving an image quality of a captured image, a method ofmanufacturing the solid-state imaging device, and an electronicapparatus.

According to an embodiment of the invention, there is provided asolid-state imaging device including an imaging area where a pluralityof unit pixels are disposed to capture a color image, wherein each ofthe unit pixels includes: a plurality of photoelectric conversionportions; a plurality of transfer gates, each of which is disposed ineach of the photoelectric conversion portions to transfer signal chargesfrom the photoelectric conversion portion; and a floating diffusion towhich the signal charges are transferred from the plurality of thephotoelectric conversion portions by the plurality of the transfergates, wherein the plurality of the photoelectric conversion portionsreceive light of the same color to generate the signal charges, andwherein the signal charges transferred from the plurality of thephotoelectric conversion portions to the floating diffusion are added tobe output as an electrical signal.

Preferably, the unit pixel is configured so that the floating diffusionsare interposed by the plurality of the photoelectric conversion portionsand so that the plurality of the transfer gates are disposed between theplurality of the photoelectric conversion portions and the floatingdiffusions.

Preferably, a plurality of the unit pixels are arrayed in a firstdirection and a second direction perpendicular to the first direction inthe imaging area; the floating diffusions are disposed so as to beinterposed by the plurality of the photoelectric conversion portions inthe first direction; and the plurality of the transfer gates aredisposed so as to be interposed between the plurality of thephotoelectric conversion portions and the floating diffusions in thefirst direction.

Preferably, a plurality of the unit pixels are arrayed in a firstdirection and a second direction perpendicular to the first direction inthe imaging area; the floating diffusions are disposed so as to beinterposed by the plurality of the photoelectric conversion portions ina direction slanted with respect to the first direction and the seconddirection; and the plurality of the transfer gates are disposed so as tobe interposed between the plurality of the photoelectric conversionportions and the floating diffusions in the direction slanted withrespect to the first direction and the second direction.

Preferably, the plurality of the photoelectric conversion portions arearrayed in the unit pixel so that the same number of the photoelectricconversion portions are aligned in each of the first direction andsecond direction.

Preferably, the plurality of the photoelectric conversion portions arearrayed so that an even number of the photoelectric conversion portionsare aligned in each of the first direction and the second direction.

Preferably, the plurality of the photoelectric conversion portions arearrayed so that multiples of the four photoelectric conversion portionsare aligned in each of the first direction and the second direction.

Preferably, the unit pixel includes: an amplification transistor ofwhich the gate is electrically connected to the floating diffusion; anda vertical signal line which outputs a signal obtained from the signalcharges transferred to the floating diffusion, wherein a plurality ofthe amplification transistors are disposed in the unit pixel, wherein aplurality of the vertical signal lines are disposed, and the pluralityof the vertical signal lines are electrically connected to each other,and wherein the signal output from the plurality of the vertical signallines are smoothed.

Preferably, the unit pixel includes: an amplification transistor ofwhich the gate is electrically connected to the floating diffusion; anda vertical signal line which outputs a signal obtained from the signalcharges transferred to the floating diffusion, wherein a plurality ofthe amplification transistors are disposed in the unit pixel, and thesources of the plurality of the amplification transistors areelectrically connected to a common vertical signal line.

Preferably, the unit pixel includes a microlens which focuses light onthe photoelectric conversion portion, and a plurality of the microlensesare disposed corresponding to the plurality of the photoelectricconversion portions.

Preferably, the unit pixel includes an optical waveguide which guideslight to the photoelectric conversion portion, and a plurality of theoptical waveguides are disposed corresponding to the plurality of thephotoelectric conversion portions.

According to another embodiment of the invention, there is provided amethod of manufacturing a solid-state imaging device including the stepof forming the solid-state imaging device by disposing a plurality ofunit pixels in an imaging area which captures a color image, wherein thestep of forming the unit pixel includes the steps of: forming aplurality of photoelectric conversion portions which receive light ofthe same color to generate signal charges; disposing a plurality oftransfer gates, which transfer the signal charges from the photoelectricconversion portions, in the plurality of the photoelectric conversionportions; and forming a floating diffusion to which signal charges fromthe plurality of the photoelectric conversion portions are transferredthrough the plurality of the transfer gates to be added.

According to still another embodiment of the invention, there isprovided an electronic apparatus having a solid-state imaging deviceincluding an imaging area where a plurality of unit pixels are disposedto capture a color image, wherein each of the unit pixels includes: aplurality of photoelectric conversion portions; a plurality of transfergates, each of which is disposed in each of the photoelectric conversionportions to transfer signal charges from the photoelectric conversionportion; and a floating diffusion to which the signal charges aretransferred from the plurality of the photoelectric conversion portionsby the plurality of the transfer gates, wherein the plurality of thephotoelectric conversion portions receive light of the same color togenerate the signal charges, and wherein the signal charges transferredfrom the plurality of the photoelectric conversion portions to thefloating diffusion are added to be output as an electrical signal.

In the invention, a plurality of unit pixels are disposed so as tocapture a color image by an imaging area. Herein, a plurality ofphotoelectric conversion portions are included in the unit pixel. Inaddition, a plurality of transfer gates which transfer signal chargesfrom each of the photoelectric conversion portions are included in theunit pixel. In addition, a floating diffusion to which the signalcharges are transferred from the plurality of the photoelectricconversion portions by the plurality of the transfer gates is includedin the unit pixel. In the invention, the plurality of the photoelectricconversion portions are formed so as to receive light of the same colorand to generate the signal charges. In addition, the signal chargestransferred from the plurality of the photoelectric conversion portionsto the floating diffusion are added to be output as an electricalsignal.

According to the invention, it is possible to provide a solid-stateimaging device capable of improving an image quality of a capturedimage, a method of manufacturing the solid-state imaging device, and anelectronic apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configurational diagram illustrating a configuration of acamera according to a first embodiment of the invention.

FIG. 2 is a diagram illustrating a whole configuration of a solid-stateimaging device according to the first embodiment of the invention.

FIG. 3 is a diagram illustrating main components of the solid-stateimaging device according to the first embodiment of the invention.

FIG. 4 is a diagram illustrating main components of the solid-stateimaging device according to the first embodiment of the invention.

FIG. 5 is a diagram illustrating main components of the solid-stateimaging device according to the first embodiment of the invention.

FIG. 6 is a diagram illustrating main components of the solid-stateimaging device according to the first embodiment of the invention.

FIG. 7 is a conceptual diagram illustrating a potential in a unit pixelaccording to the first embodiment of the invention.

FIGS. 8A to 8C are timing charts illustrating pulse signals supplied toportions of the unit pixel when a signal is read out from the unit pixelaccording to the first embodiment of the invention.

FIG. 9 is a diagram illustrating main components formed in processes ofa method of manufacturing the solid-state imaging device according tothe first embodiment of the invention.

FIG. 10 is a diagram illustrating main components formed in processes ofa method of manufacturing the solid-state imaging device according tothe first embodiment of the invention.

FIG. 11 is a diagram illustrating a behavior of incident light incidenton the unit pixel according to the first embodiment of the invention.

FIG. 12 is a diagram illustrating a behavior of incident light incidenton the unit pixel according to the first embodiment of the invention.

FIG. 13 is a diagram illustrating main components of a solid-stateimaging device according to a second embodiment of the invention.

FIG. 14 is a diagram illustrating main components of a solid-stateimaging device according to a third embodiment of the invention.

FIG. 15 is a diagram illustrating main components of the solid-stateimaging device according to the third embodiment of the invention.

FIG. 16 is a diagram illustrating main components of the solid-stateimaging device according to the third embodiment of the invention.

FIG. 17 is a diagram illustrating main components of a solid-stateimaging device according to a fourth embodiment of the invention.

FIG. 18 is a diagram illustrating an array of unit pixels in a CMOS typeimage sensor.

FIGS. 19A and 19B are conceptual diagrams illustrating a potential inthe unit pixel in the CMOS type image sensor.

FIG. 20 is a diagram illustrating a behavior of incident light incidenton the unit pixel of the CMOS type image sensor.

FIG. 21 is a diagram illustrating a behavior of incident light incidenton the unit pixel of the CMOS type image sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the invention will be described withreference to the drawings.

In addition, the description will be made in the following order.

1. First Embodiment (a case where a unit pixel includes 4 PDs)

2. Second Embodiment (a case where there is an optical wave guide)

3. Third Embodiment (a case where a unit pixel includes 16 PDs)

4. Fourth Embodiment (a case where a unit pixel includes 16 PDs)

5. Others

1. First Embodiment (A) Configuration of Apparatus

(A-1) Configuration of Main Components of Camera

FIG. 1 is a configurational diagram illustrating a configuration of acamera 40 according to a first embodiment of the invention.

As illustrated in FIG. 1, the camera 40 is an electronic apparatus andincludes a solid-state imaging device 1, an optical system 42, acontroller 43, and a signal processing circuit 44.

The solid-state imaging device 1 generates signal charges by receivingincident light H incident as a subject image through the optical system42 by an imaging plane PS and photoelectrically converting the light. Inaddition, the solid-state imaging device 1 is driven based on a controlsignal output from the controller 43 to read out the signal charges andoutput raw data.

In the embodiment, as illustrated in FIG. 1, in the solid-state imagingdevice 1, main light beams H1 emitted from the optical system 42 areincident on the central portion of the imaging plane PS at an angleperpendicular to the imaging plane PS. On the other hand, main lightbeams H21 and H22 are incident on the peripheral portion of the imagingplane PS at an angle slanted with respect to the direction perpendicularto the imaging plane PS of the solid-state imaging device 1. Herein, themain light beams H21 and H22 are slantingly incident on the imagingplane PS from the center of the imaging plane PS toward the peripherythereof.

The optical system 42 includes optical elements such as a focusing lensor an aperture. The optical system 42 is disposed so that incident lightaccording to a subject image is focused on the imaging plane PS of thesolid-state imaging device 1.

In the embodiment, the optical system 42 is installed so that theoptical axis corresponds to the center of the imaging plane PS of thesolid-state imaging device 1. Therefore, as illustrated in FIG. 1, theoptical system 42 emits the main light beams H1 to the central portionof the imaging plane PS of the solid-state imaging device 1 at the angleperpendicular to the imaging plane PS. On the other hand, the opticalsystem 42 emits the main light beams H21 and H22 to the peripheralportion of the imaging plane PS at an angle slanted with respect to thedirection perpendicular to the imaging plane PS. This is caused byfiniteness of an exit pupil distance formed by an aperture or the like.

The controller 43 outputs various control signals to the solid-stateimaging device 1 and the signal processing circuit 44 to control anddrive the solid-state imaging device 1 and the signal processing circuit44.

The signal processing circuit 44 is configured to generate a digitalimage with respect to the subject image by performing a signal processon raw data output from the solid-state imaging device 1.

(A-2) Main Components of Solid-State Imaging Device

A whole configuration of the solid-state imaging device 1 is described.

FIG. 2 is a diagram illustrating a whole configuration of thesolid-state imaging device 1 according to the first embodiment of theinvention. In FIG. 2, an upper surface is illustrated.

The solid-state imaging device 1 according to the embodiment is a CMOStype image sensor and includes a semiconductor substrate 101 asillustrated in FIG. 2. The semiconductor substrate 101 is, for example,a semiconductor substrate made of silicon and, as illustrated in FIG. 2,an imaging area PA and a peripheral area SA are disposed in a surface ofthe semiconductor substrate 101.

As illustrated in FIG. 2, the imaging area PA has a quadrangular shape,in which a plurality of the unit pixels P are disposed in each of thehorizontal direction x and the vertical direction y. In other words, theunit pixels P are aligned in a matrix shape. In addition, the imagingarea PA is disposed so that the center thereof corresponds to theoptical axis of the optical system 42 illustrated in FIG. 1.

The imaging area PA corresponds to the imaging plane PS illustrated inFIG. 1. Therefore, as described above, in the unit pixel P disposed atthe central portion of the imaging area PA, the main light beams (H1 ofFIG. 1) are incident at an angle perpendicular to the plane of theimaging area PA. On the other hand, in the unit pixel P (for example,the upper pixel PU or the lower pixel PL) disposed in the peripheralportion of the imaging area PA, the main light beam (H21 or H22 ofFIG. 1) is incident at an angle slanted with respect to the directionperpendicular to the plane of the imaging area PA.

As illustrated in FIG. 2, the peripheral area SA is located in theperiphery of the imaging area PA. In addition, peripheral circuits aredisposed in the peripheral area SA.

More specifically, as illustrated in FIG. 2, a vertical driving circuit13, a column circuit 14, a horizontal driving circuit 15, an externaloutput circuit 17, and a timing generator (TG) 18 are disposed as theperipheral circuits.

As illustrated in FIG. 2, the vertical driving circuit 13 is configuredto be disposed at a side portion of the imaging area PA in theperipheral area SA so as to select and drive the unit pixels P of theimaging area PA in units of a row of the unit pixels P.

As illustrated in FIG. 2, the column circuit 14 is configured to bedisposed in the lower end portion of the imaging area PA in theperipheral area SA so as to perform a signal process on the signaloutput from the unit pixels P in units of a column of the unit pixels P.Herein, the column circuit 14 includes a CDS (Correlated DoubleSampling) circuit (not shown) to perform a signal process of removingfixed pattern noise.

As illustrated in FIG. 2, the horizontal driving circuit 15 iselectrically connected to the column circuit 14. The horizontal drivingcircuit 15 includes, for example, shift registers to sequentially outputsignals stored in units of a column of the unit pixels P in the columncircuit 14 to the external output circuit 17.

As illustrated in FIG. 2, the external output circuit 17 is electricallyconnected to the column circuit 14. The external output circuit 17performs a signal process on the signal output from the column circuit14 and outputs the processed signal to an external portion. The externaloutput circuit 17 includes an AGC (Automatic Gain Control) circuit 17 aand an ADC circuit 17 b. In the external output circuit 17, the AGCcircuit 17 a applies a gain to a signal, and after that, the ADC circuit17 b converts an analog signal to a digital signal to output the digitalsignal to an external portion.

As illustrated in FIG. 2, the timing generator 18 is electricallyconnected to the vertical driving circuit 13, the column circuit 14, thehorizontal driving circuit 15, and the external output circuit 17. Thetiming generator 18 generates various timing signals and outputs thetiming signals to the vertical driving circuit 13, the column circuit14, the horizontal driving circuit 15, and the external output circuit17 to perform driving controls of the portions.

(A-3) Detailed Configuration of Solid-State Imaging Device

A detailed configuration of the solid-state imaging device 1 accordingto the embodiment is described.

FIGS. 3 to 6 are diagrams illustrating main components of thesolid-state imaging device 1 according to the first embodiment of theinvention.

Herein, FIG. 3 illustrates an upper surface of an imaging area PA wherea plurality of the unit pixels P are arrayed in the solid-state imagingdevice 1. In FIG. 3 a portion where two unit pixels P in each of thehorizontal direction x and the vertical direction y are aligned to beadjacent to each other is exemplarily illustrated.

In addition, FIG. 4 illustrates an upper surface of one unit pixel P. InFIG. 4, the upper surface of the unit pixel P (red pixel) where the redfilter layer CFR in FIG. 3 is disposed is exemplarily illustrated. Inaddition, in FIG. 3, the unit pixel P (green pixel) where the greenfilter layer CFG is disposed and the unit pixel P (blue pixel) where theblue filter layer CFB is disposed also have the same configuration asthe unit pixel P (red pixel) where the red filter layer CFR is disposed.

In addition, FIG. 5 illustrates a circuit configuration of one unitpixel P. In FIG. 5, similarly to FIG. 4, a circuit configuration of theunit pixel P (red pixel) where the red filter layer CFR in FIG. 3 isdisposed is exemplarily illustrated. In addition, the green pixel andthe blue pixel also have the same configuration as the red pixel.

In addition, FIG. 6 illustrates a cross section of one unit pixel P. InFIG. 6, a cross section of a portion taken along line VI-VI of FIG. 4 isillustrated.

(A-3-1) Array of Unit Pixels

As illustrated in FIG. 3, in the solid-state imaging device 1, aplurality of the unit pixels P are disposed in each of the horizontaldirection x and the vertical direction y.

As illustrated in FIG. 3, in the solid-state imaging device 1, in orderto capture a color image, each color filter CF is disposed in each ofthe unit pixels P. The color filter CF includes a red filter layer CFR,a green filter layer CFG, and a blue filter layer CFB. The red filterlayer CFR, the green filter layer CFG, and the blue filter layer CFB areadjacent to each other, and one thereof is disposed corresponding toeach of the unit pixels P.

Herein, as illustrated in FIG. 3, the red filter layer CFR, the greenfilter layer CFG, and the blue filter layer CFB are disposed to bealigned in a Bayer array. In other words, a plurality of the greenfilter layers CFG are disposed to be aligned in the diagonal directionso as to be in a checkered shape. In addition, the red filter layers CFRand the blue filter layers CFB are disposed to be aligned in thediagonal direction of the plurality of the green filter layers CFG.

In addition, although not shown, a light blocking portion (not shown) isdisposed in the periphery of each of the red filter layer CFR, the greenfilter layer CFG, and the blue filter layer CFB so as to partition theunit pixel P.

In the embodiment, as illustrated in FIG. 3, each unit pixel P includesa plurality of the imaging portions PA1, PA2, PB1, and PB2. In theembodiment, the unit pixel P is configured to include four imagingportions PA1, PA2, PB1, and PB2.

(A-3-2) Each Unit Pixel

As illustrated in FIGS. 4 and 5, in the unit pixel P, a plurality of theimaging portions PA1, PA2, PB1, and PB2 are arrayed on the imaging plane(xy plane).

The plurality of the imaging portions PA1, PA2, PB1, and PB2 are alignedon the imaging plane (xy plane) in the horizontal direction x and thevertical direction y perpendicular to the horizontal direction x.

As illustrated in FIGS. 4 and 5, in each of the imaging portions PA1,PA2, PB1, and PB2, a photodiode 21 and a transfer transistor 22 aredisposed. In addition, under the plurality of the imaging portions PA1,PA2, PB1, and PB2, a transistor group constructed as a set of anamplification transistor 23, a selection transistor 24, and a resettransistor 25 is disposed. In other words, the unit pixel P isconstructed so that the four imaging portions PA1, PA2, PB1, and PB2,each of which includes the photodiode 21 and the transfer transistor 22,share the set of the amplification transistor 23, the selectiontransistor 24, and the reset transistor 25.

More specifically, as illustrated in FIG. 4, in the area partitionedinto the two imaging portions PA1 and PA2 aligned in the verticaldirection y, the two photodiodes 21 are disposed so as to be aligned inthe vertical direction y in each of the imaging portions PA1 and PA2. Inaddition, between the photodiodes 21, the transfer gates 22G of the twotransfer transistors 22 are disposed so as to be aligned in the verticaldirection y in each of the imaging portions PA1 and PA2. In addition,the floating diffusion FD is disposed between the two transfer gates 22Galigned in the vertical direction y.

In addition, as illustrated in FIG. 4, the two imaging portions PB1 andPB2 aligned in the vertical direction y are disposed in the sameconfiguration as that of the two imaging portions PA1 and PA2. In otherwords, sets constructed with the two photodiodes 21, the two transfergates 22G, and the floating diffusion FD aligned in the verticaldirection y are disposed so as to be aligned in the horizontal directionx.

Herein, as illustrated in FIG. 5, the floating diffusions FD aligned inthe horizontal direction x are electrically connected to each otherthrough a wire line Hab, and the floating diffusions FD are connected tothe gate of the amplification transistor 23.

Besides, as illustrated in FIGS. 4 and 6, in the unit pixel P, amicrolens ML is disposed.

As illustrated in FIG. 6, in the unit pixel P, the wire-line layer 111and the color filter CF are disposed between the microlens ML and thephotodiode 21, so that the incident light H incident sequentiallythrough these components is received by the photodiode 21.

In addition, as illustrated in FIG. 5, in the unit pixel P, the transfertransistor 22 transfers the signal charges generated by the photodiode21 to the floating diffusions FD to output an electrical signal throughthe amplification transistor 23 or the like to the vertical signal line27.

The detail configurations of the components constituting the unit pixelP are sequentially described.

(a) Photodiode

As illustrated in FIG. 4, in the unit pixel P, a plurality of thephotodiodes 21 are disposed on the imaging plane (xy plane). The evennumber of the photodiodes 21 are disposed to be aligned in each of thehorizontal direction x and the vertical direction y to correspond to thearray of the imaging portions PA1, PA2, PB1, and PB2. For example, thephotodiode 21 is disposed in each of the imaging portions PA1, PA2, PB1,and PB2, of which the size is in a range of from 1 to 2 μm. In otherwords, the photodiodes 21 are disposed so that the two photodiodes 21are aligned in an equal interval in each of the horizontal direction xand the vertical direction y.

As illustrated in FIG. 6, the photodiodes 21 are disposed in thesemiconductor substrate 101.

The photodiode 21 is configured so as to generate and accumulate thesignal charges by receiving the incident light H incident as a subjectimage with the light-receiving plane JS and photoelectrically convertingthe incident light H.

For example, the photodiode 21 is configured so that an n-type chargeaccumulation area (not shown) is formed in a p well (not shown) disposedin the semiconductor substrate 101 which is an n-type siliconsemiconductor. In addition, furthermore, in order to suppress a darkcurrent, a p-type accumulation layer (not shown) is configured to beincluded on the front surface of the semiconductor substrate 101. Inother words, the photodiode 21 is formed in a so-called HAD (HallAccumulated Diode) structure.

In addition, as illustrated in FIG. 5, each of the photodiodes 21 isconfigured so that the accumulated signal charges are transferred to thefloating diffusion FD by the transfer transistor 22.

In the embodiment, as illustrated in FIGS. 4 and 5, the unit pixel Pincludes the four photodiodes 21, and the four transfer transistors 22corresponding to the four photodiodes 21 are disposed in pairs. Herein,the transfer transistor 22 is disposed between the two photodiodes 21aligned in the vertical direction y. In addition, the floating diffusionFD is disposed between the two transfer transistors 22 disposed betweenthe two photodiodes 21 aligned in the vertical direction y.

In addition, as illustrated in FIG. 5, in the unit pixel P, the fourphotodiodes 21 are configured so as to share a set of an amplificationtransistor 23, a selection transistor 24, and a reset transistor 25. Inother words, with respect to the four photodiodes 21, one amplificationtransistor 23, one selection transistor 24, and one reset transistor 25are disposed.

(b) Transistors

As illustrated in FIG. 4, in the unit pixel P, a transfer transistor 22,an amplification transistor 23, a selection transistor 24, and a resettransistor 25 are disposed on the imaging plane (xy plane). The transfertransistor 22, the amplification transistor 23, the selection transistor24, and the reset transistor 25 are configured so that signal chargesgenerated in the photodiode 21 are read out to be output as a datasignal.

Each of the transfer transistor 22, the amplification transistor 23, theselection transistor 24, and the reset transistor 25 is configured with,for example, an N-channel MOS transistor.

Detailed Configurations of the transistors are sequentially described.

(b-1) Transfer Transistor

As illustrated in FIG. 4, in the unit pixel P, a plurality of thetransfer transistors 22 are disposed in each of the horizontal directionx and the vertical direction y so as to correspond to a plurality of theimaging portions PA1, PA2, PB1, and PB2.

Herein, as illustrated in FIG. 4, the transfer transistors 22 aredisposed so that the two transfer transistors 22 interpose the floatingdiffusion FD disposed between the plurality of the photodiodes 21aligned in the vertical direction y on the imaging plane (xy plane).

As illustrated in FIG. 4, each transfer transistor 22 includes atransfer gate 22G, and the transfer gate 22G is disposed to extend inthe horizontal direction x. In addition, the transfer gate 22G isdisposed between the photodiodes 21 aligned in the vertical direction yin the unit pixel P.

As illustrated in FIG. 6, the transfer gates 22G are disposed on thefront surface of the semiconductor substrate 101. Although not shown, agate insulating film (not shown) is interposed between the transfer gate22G and the front surface of the semiconductor substrate 101. Inaddition, the transfer gates 22G are disposed to be adjacent to thefloating diffusions FD disposed on the surface layer of thesemiconductor substrate 101 so that the two transfer gates 22G interposeone floating diffusion FD. The transfer gates 22G is formed with, forexample, a conductive light-blocking material such as polysilicon.

As illustrated in FIG. 5, the transfer transistor 22 is configured so asto transfer the signal charges accumulated in the photodiode 21 as anoutput signal to the floating diffusion FD by applying a transfer signalfrom the transfer line 26 to the gate of the transfer transistor 22.

Herein, as illustrated in FIG. 5, the one terminal of the transfertransistor 22 is electrically connected to the cathode of the photodiode21. In addition, the other terminal of the transfer transistor 22 iselectrically connected to one floating diffusion FD.

In the embodiment, a pair of the transfer transistors 22 aligned in thevertical direction y are configured to transfer the signal charges tothe floating diffusion FD. Therefore, the signal charges of a pair ofthe transfer transistors 22 aligned in the vertical direction y areadded to the floating diffusion FD and output to the gate of theamplification transistor 23.

(b-2) Amplification Transistor

As illustrated in FIG. 4, in the unit pixel P, the amplificationtransistor 23 is disposed on the imaging plane (xy plane) under theplurality of the imaging portions PA1, PA2, PB1, and PB2. In otherwords, the amplification transistor 23 is disposed on the imaging plane(xy plane) under the plurality of the photodiodes 21 aligned in thehorizontal direction x and the vertical direction y. Herein, theamplification transistor 23 is disposed so that a pair of the source andthe drain interposes the channel in the horizontal direction.

As illustrated in FIG. 5, the amplification transistor 23 is configuredto amplify and output the electrical signal output from the transfertransistor 22.

More specifically, as illustrated in FIG. 5, the gate of theamplification transistor 23 is connected to the floating diffusion FD.In addition, the drain of the amplification transistor 23 is connectedto the power supply voltage Vdd, and the source thereof is connectedthrough the selection transistor 24 to the vertical signal line 27. Whenthe selection transistor 24 is selected so as to be in the on state, theamplification transistor 23 is supplied with a constant current from aconstant current source I, so that the amplification transistor 23operates as a source follower. Therefore, when a selection signal issupplied to the selection transistor 24, the output signal output fromthe floating diffusion FD is amplified by the amplification transistor23.

(b-3) Selection Transistor

As illustrated in FIG. 4, in the unit pixel P, the selection transistor24 is disposed on the imaging plane (xy plane) under the plurality ofthe imaging portions PA1, PA2, PB1, and PB2. In other words, similarlyto the amplification transistor 23, the selection transistor 24 isdisposed on the imaging plane (xy plane) under the plurality of thephotodiodes 21 aligned in the horizontal direction x and the verticaldirection y. Herein, the selection transistor 24 is disposed so that apair of the source and the drain interposes the channel in thehorizontal direction.

As illustrated in FIG. 5, the selection transistor 24 is configured soas to output the electrical signal output by the amplificationtransistor 23 to the vertical signal line 27 when the selection signalis input.

More specifically, as illustrated in FIG. 5, the gate of the selectiontransistor 24 is connected to the address line 28 supplied with theselection signal. When the selection signal is supplied, the selectiontransistor 24 is turned on to output the output signal, which isamplified by the amplification transistor 23 as described above, to thevertical signal line 27.

(b-4) Reset Transistor

As illustrated in FIG. 4, in the unit pixel P, the reset transistor 25is disposed on the imaging plane (xy plane) under the plurality of theimaging portions PA1, PA2, PB1, and PB2. In other words, similarly tothe amplification transistor 23 and the selection transistor 24, thereset transistor 25 is disposed on the imaging plane (xy plane) underthe plurality of the photodiodes 21 aligned in the horizontal directionx and the vertical direction y. Herein, the reset transistor 25 isdisposed so that a pair of the source and the drain interposes thechannel in the horizontal direction.

As illustrated in FIG. 5, the reset transistor 25 is configured so as toreset the potential of the gate of the amplification transistor 23.

More specifically, as illustrated in FIG. 5, the gate of the resettransistor 25 is connected to the reset line 29 supplied with the resetsignal. In addition, the drain of the reset transistor 25 is connectedto the power supply voltage Vdd, and the source thereof is connected tothe floating diffusion FD. In addition, when the reset signal issupplied from the reset line 29 to the gate, the reset transistor 25resets the potential of the gate of the amplification transistor 23 tothe power supply voltage Vdd through the floating diffusion FD.

(c) Wire-Line Layer 111

As illustrated in FIG. 6, the wire-line layer 111 is disposed on thefront surface of the semiconductor substrate 101 where the transfergates 22G of the transfer transistors 22 are disposed.

The wire-line layer 111 includes wire lines (not shown), and the wirelines in the insulating layer are formed so as to be electricallyconnected to elements. Herein, the wire lines are formed throughlamination in the insulating layer so as to function as wire lines suchas a transfer line 26, an address line 28, a vertical signal line 27,and a reset line 29 illustrated in FIG. 5.

More specifically, in the wire-line layer 111, in the boundary portionof the unit pixel P or in the boundary portion where the plurality ofthe imaging portions PA1, PA2, PB1, and PB2 constituting the unit pixelP are aligned, the wire lines are disposed.

(d) Color Filter CF

As illustrated in FIG. 6, the color filter CF is disposed at the side ofthe front surface of the semiconductor substrate 101 where the transfergates 22G of the transfer transistors 22 are disposed.

Herein, as illustrated in FIG. 6, the color filter CF is disposed on theupper surface of the wire-line layer 111. In addition, the microlensesML are disposed on the upper surface of the color filter CF.

As illustrated in FIG. 6, the color filter CF is configured so as tocolor the incident light according to the subject image to betransmitted through the light-receiving plane JS of the semiconductorsubstrate 101.

As illustrated in FIG. 3, the color filter CF includes a red filterlayer CFR, a green filter layer CFG, and a blue filter layer CFB and isdisposed in a Bayer array so as to correspond to each of the unit pixelsP.

More specifically, in the color filter CF, the red filter layer CFR isconfigured to have high light transmittance with respect to thewavelength range (for example, a range of from 625 to 740 nm)corresponding to red and to color the incident light with red to betransmitted through the light-receiving plane. The red filter layer CFRis formed so that the plane structure thereof is a quadrangular shape.

In addition, in the color filter CF, the green filter layer CFG isconfigured to have high light transmittance with respect to thewavelength range (for example, a range of from 500 to 565 nm)corresponding to green and to color the incident light with green to betransmitted through the light-receiving plane. The green filter layerCFG is formed so that the plane structure thereof is a quadrangularshape.

In the color filter CF, the blue filter layer CFB is configured to havehigh light transmittance with respect to the wavelength range (forexample, a range of from 450 to 485 nm) corresponding to blue and tocolor the incident light with blue to be transmitted through thelight-receiving plane. The blue filter layer CFB is formed so that theplane structure thereof is a quadrangular shape.

In addition, as illustrated in FIG. 3, the color filter CF is configuredso that the same color filter layers CFR, CFG, and CFB are disposed inthe plurality of the imaging portions PA1, PA2, PB1, and PB2constituting the unit pixel P. For example, as illustrated in FIG. 3, inthe unit pixel P located at the left lower portion among the four unitpixels P, the red filter layer CFR is disposed in the plurality of theimaging portions PA1, PA2, PB1, and PB2 constituting the unit pixel P.As illustrated in FIG. 6, in the imaging portions PA1, PA2, PB1, andPB2, the red filter layer CFR are integrally formed.

For example, the color filter CF is formed by forming a coated layer bycoating a coating solution including a coloring pigment and aphotoresist resin according to a coating method such as a spin coatingmethod, and after that, performing a pattern process on the coated layeraccording to a lithography technology.

(e) Microlens ML

As illustrated in FIG. 6, the microlenses ML are disposed at the side ofthe front surface of the semiconductor substrate 101 where the transfergates 22G of the transfer transistors 22 are disposed.

Herein, as illustrated in FIG. 6, the microlenses ML are disposed on theupper surface of the color filter CF. A plurality of the microlenses MLare disposed so as to correspond to the plurality of the imagingportions PA1, PA2, PB1, and PB2 constituting the unit pixel P.

As illustrated in FIG. 6, the microlens ML is disposed above thelight-receiving plane JS. The microlens ML is a convex lens of which thecenter is thicker than the edge and is configured to focus the incidentlight H to the light-receiving plane JS of the photodiode 21.

For example, the microlens ML is formed by using a transparent organicmaterial such as a styrene resin, an acrylic resin, and a novolac resin.Besides, the microlens ML may be formed by using a transparent inorganicmaterial such as SiO₂, SiN, SiON, SiCN, and HfO.

(f) Others

FIG. 7 is a conceptual diagram illustrating a potential in the unitpixel P according to the first embodiment of the invention. In FIG. 7, apotential in a portion taken along line VII-VII of FIG. 4 isillustrated.

As illustrated in FIG. 7, in the embodiment, similarly to the caseillustrated in FIG. 19B, the electric field gradient in the photodiode21 is formed to be increased so that the signal charges are moved to theside of the transfer transistor 22.

FIGS. 8A to 8C are timing charts illustrating pulse signals supplied toportions of the unit pixel P when a signal is read out from the unitpixel P according to the first embodiment of the invention. FIG. 8Aillustrates a selection signal (SEL); FIG. 8B illustrates a reset signal(RST); and FIG. 8C illustrates transfer signals (TRF1 and TRF2) (referto FIG. 5)

First, as illustrated in FIGS. 8A to 8C, at the first time point t1, theselection transistor 24 is set to a conduction state. In addition, atthe second time point t2, the reset transistor 25 is set to a conductionstate. Therefore, the potential of the gate of the amplificationtransistor 23 is reset.

Next, at the third time point t3, the reset transistor 25 is set to anon-conduction state. In addition, after that, the voltage correspondingto the reset level is read out as the output signal to the columncircuit 14.

Next, at the fourth time point t4, the transfer transistor 22 is set toa conduction state, so that the signal charges accumulated in thephotodiode 21 are transferred to the gate of the amplificationtransistor 23.

Next, at the fifth time point t5, the transfer transistor 22 is set to anon-conduction state. In addition, after that, the voltage correspondingto the signal level according to the amount of the accumulated signalcharges is read out as the output signal to the column circuit 14.

In the column circuit 14, a differencing process is performed on theformer-read reset level and the latter-read signal level, so that thesignal is accumulated. Accordingly, fixed pattern noise generatedaccording to the irregularity or the like of the Vth of each transistordisposed in each unit pixel P is cancelled.

Since the gates of the transistors 22, 24, and 25 are connected in unitsof a row constructed with the plurality of the unit pixels P aligned inthe horizontal direction x, the aforementioned operation of driving theunit pixel P is simultaneously performed with respect to the pluralityof the unit pixels P aligned in units of a row.

More specifically, the unit pixels P are sequentially selected in thevertical direction in units of a horizontal line (pixel row) accordingto the selection signal supplied by the aforementioned vertical drivingcircuit 13. In addition, the transistors of the unit pixels P arecontrolled according to various timing signals output from the timinggenerator 18. Therefore, the output signal of each of the unit pixels Pis output to the column circuit 14 through the vertical signal line 27in each column of the unit pixels P.

In addition, the signals accumulated in the column circuit 14 areselected by the horizontal driving circuit 15 to be sequentially outputto the external output circuit 17.

In the embodiment, the signal charges generated by the plurality of theimaging portions PA1, PA2, PB1, and PB2 constituting the unit pixel Pare added to be output as the output signal to the vertical signal line27.

For example, as illustrated in FIGS. 8A to 8C, the signal charges of thephotodiodes 21 disposed in the four imaging portions PA1, PA2, PB1, andPB2 are transferred through the transfer transistors 22 to the floatingdiffusion FD at the same timing. In addition, the voltage of the signallevel according to the amount of the signal charges added in thefloating diffusion FD is read out as the output signal.

In addition, the signal charges of the photodiodes 21 may besequentially transferred to the floating diffusion FD at differenttimings, and the output signal may be driven so as to be read out basedon the signal charges added in the floating diffusion FD.

(B) Method of Manufacturing Solid-State Imaging Device

Hereinafter, main processes of a method of manufacturing theaforementioned solid-state imaging device 1 are described.

FIGS. 9 and 10 are diagrams illustrating main components formed inprocesses of a method of manufacturing the solid-state imaging device 1according to the first embodiment of the invention. Herein, FIGS. 9 and10 illustrate a cross section of the imaging area PA similarly to FIG.6.

(B-1) Formation of Photodiode 21, Transfer Transistor 22, and FloatingDiffusion FD

First, as illustrated in FIG. 9, the photodiode 21, the transfertransistor 22, and the floating diffusion FD are formed.

The photodiode 21 is formed by disposing an n-type charge accumulationarea in a p well (not shown) disposed in the semiconductor substrate 101which is an n-type silicon semiconductor. In addition, furthermore, ahigh-concentration p-type accumulation layer (not shown) is formed onthe surface of the n-type charge accumulation area. More specifically,components constituting the photodiode 21 are disposed by appropriatelyinjecting impurity ions into the semiconductor substrate 101.

The transfer transistor 22 is formed by forming a gate insulating film(not shown) on an upper surface of a channel formation area and, afterthat, by disposing a transfer gate 22G on an upper surface of the gateinsulating film. More specifically, a silicon oxide film (not shown) isformed as the gate insulating film by performing a thermal oxidationprocess on the surface of the semiconductor substrate 101. In addition,for example, after a polysilicon film (not shown) is formed on the gateinsulating film, a patterning process is performed on the polysiliconfilm (not shown), so that the transfer gate 22G is formed.

At the time of forming the transfer transistor 22, other transistorsincluding the amplification transistor 23, the selection transistor 24,and the reset transistor 25 are formed in a similar manner.

The floating diffusion FD is formed by injecting n-type impurity ionsinto an upper layer of the semiconductor substrate 101. At the time offorming the floating diffusion FD, the source and drain regions of eachtransistor are also formed in a similar manner.

(B-2) Formation of Wire-Line Layer 111

Next, as illustrated in FIG. 10, the wire-line layer 111 is formed.

Herein, as illustrated in FIG. 10, in the semiconductor substrate 101,the wire-line layer 111 is disposed on the surface where the transfergate 22G of the transfer transistor 22 is disposed.

For example, the wire-line layer 111 is disposed by forming aninsulating layer by using an insulating material such as silicon oxidefilm and, at the same time, by forming a wire line (not shown) by usinga metal material such as aluminum.

(B-3) Formation of Color Filter CF and Microlens ML

Next, as illustrated in FIG. 6, the color filter CF and the microlens MLare formed.

Herein, as illustrated in FIG. 6, the color filter CF is disposed on thesurface where the wire-line layer 111 is coated in the semiconductorsubstrate 101. In addition, a microlens ML is disposed on the colorfilter CF.

In this manner, the components are disposed, so that the solid-stateimaging device 1 is completed as a CMOS type image sensor.

(C) Conclusion

In this manner, in the solid-state imaging device 1 according to theembodiment, a plurality of the unit pixels P are disposed in the imagingarea PA which captures a color image. A plurality of the unit pixels Pare disposed in the imaging area PA in each of the horizontal directionx and the vertical direction y. The unit pixels P are disposed in aBayer array in the imaging area PA so as to receive light of each ofthree primary colors. In other words, in the pixel array, the unitpixels P of red and the unit pixels P of green aligned in the verticaldirection y to be adjacent to the unit pixels P of red are arrayed atthe left side. In addition, the unit pixels P of green and the unitpixels P of blue aligned in the vertical direction y to be adjacent tothe unit pixels P of green are arrayed at the right side (refer to FIG.3).

A plurality of the photodiodes 21 (photoelectric conversion portions)are arrayed in each of the unit pixels P so as to receive light of thesame color and generate the signal charges. In addition, a plurality ofthe transfer gates 22G which transfer the signal charges from thephotodiodes 21 are formed by using a light blocking material forblocking light to be disposed in the plurality of the photodiodes 21. Inaddition, the signal charges from the plurality of the photodiodes 21are configured so as to be transferred by the plurality of the transfergates 22G to the floating diffusion FD to be added (refer to FIG. 4).

More specifically, in each of the unit pixels P, the photodiodes 21 aredisposed in each of the imaging portions PA1 and PB1 (sub pixels)aligned in the horizontal direction x. In addition, the photodiodes 21are disposed in each of the imaging portions PA2 and PB2 aligned in thevertical direction y of the imaging portions PA1 and PB1. In the unitpixel P, the photodiodes 21 are arrayed so that the same number of thephotodiodes are aligned in each of the horizontal direction x and thevertical direction y (refer to FIG. 4).

In addition, in each of the unit pixels P, the transfer gates 22G whichtransfer the signal charges from the photodiodes 21 to the floatingdiffusion FD are disposed in the imaging portions PA1 and PB1 aligned inthe horizontal direction x. In addition, the transfer gates 22G whichtransfer the signal charges from the photodiodes 21 to the floatingdiffusion FD are disposed in the imaging portions PA2 and PB2 aligned inthe vertical direction y of the imaging portions PA1 and PB1 (refer toFIG. 4).

In the unit pixel P, the floating diffusions FD are disposed between thephotodiodes 21 of the imaging portions PA1 and PB1 and the photodiodes21 of the imaging portions PA2 and PB2 aligned in the vertical directiony. In addition, the floating diffusions FD are disposed between thetransfer gates 22G of the imaging portions PA1 and PB1 and the transfergates 22G of the imaging portions PA2 and PB2 aligned in the verticaldirection y (refer to FIG. 4).

Therefore, in the solid-state imaging device according to theembodiment, it is possible to prevent the occurrence of the colorshading, so that it is possible to improve the image quality of thecolor image.

Hereinafter, the aforementioned configurations will be described indetail.

FIGS. 11 and 12 are diagrams illustrating behaviors of incident lightincident on the unit pixel P according to the first embodiment of theinvention.

Herein, FIG. 11 illustrates a behavior of main light beams H21 incidenton upper pixels PU located in the upper end portion of the imaging areaPA where the plurality of the unit pixels P are disposed. In addition,FIG. 12 illustrates a behavior of main light beams H22 incident on lowerpixels PL located in the lower end portion of the imaging area PA wherethe plurality of the unit pixels P are disposed (refer to FIG. 2). Inaddition, for simplifying the description, in FIGS. 11 and 12, thedescription of the wire-line layer 111 and the like is omitted.

As illustrated in FIGS. 11 and 12, the main light beams H21 and H22 areincident on the upper pixels PU or the lower pixels PL of the imagingarea PA not in the direction z perpendicular to the imaging plane (xyplane) of the semiconductor substrate 101 but in the direction slantedwith respect to the direction z (refer to FIGS. 1, 2, and the like)

Herein, as illustrated in FIG. 6, in the unit pixel P, since the redfilter layer CFR (not shown in FIGS. 11 and 12) is disposed above eachof the imaging portions PA1 and PA2, the main light beams H21 and H22are incident as red light to the photodiodes 21.

Therefore, as illustrated in FIG. 11, in the imaging portion PA2 (theupper portion in FIG. 4) illustrated at the right side in the upperpixels PU located in the upper end portion of the imaging area PA, aportion of the main light beams H21 as red light is blocked by thetransfer gates 22G before the main light beams H21 are incident on thephotodiodes 21. On the other hand, in the imaging portion PA1illustrated at the left side, the main light beams H21 as red light arenot blocked by the transfer gates 22G before the main light beams H21are incident on the photodiodes 21.

On the contrary, as illustrated in FIG. 12, in the imaging portion PA1illustrated at the left side in the lower pixels PL located in the lowerend portion of the imaging area PA, a portion of the main light beamsH21 as red light is blocked by the transfer gates 22G before the mainlight beams H21 are incident on the photodiodes 21. On the other hand,in the imaging portion PA2 illustrated at the right side, the main lightbeams H21 as red light are not blocked by the transfer gates 22G beforethe main light beams H21 are incident on the photodiodes 21.

In this manner, the vignetting ratios of red light in the upper endportion and the lower end portion of the imaging area PA are the same.In other words, in the unit pixel P, the portions where the photodiodes21, the transfer gates 22G, and the floating diffusions FD are disposedare formed so as to be symmetric with respect to the horizontaldirection x and the vertical direction y as axes. Therefore, since thepositions where the transfer gates 22G are disposed in the upper portionand the lower portion of the imaging area PA are symmetric with respectto the photodiode 21 which receive the red light, the vignetting ratiosof the red light in the upper portion and the lower portion of theimaging area PA are the same.

Besides the red light, with respect to the blue light and the greenlight, similarly to the red light, the transfer gates 22G of the upperpixel PU and the lower pixel PL are disposed so that the vignettingratios of the red light in the upper end portion and the lower endportion of the imaging area PA are the same.

Therefore, in the embodiment, as described above, it is possible toprevent the occurrence of the color shading, so that it is possible toimprove the image quality of the color image.

Particularly, in the case where the solid-state imaging device is usedin a small-sized electronic apparatus such as a capsule endoscope or aportable camera, as described above, the considerable color shadingoccurs. However, in the case according to the embodiment, it is possibleto effectively prevent the occurrence of the problem.

In addition, in the embodiment, the unit pixel P is configured with aplurality of the imaging portions PA1, PA2, PB1, and PB2. Therefore,although the area of the unit pixel P is allowed to be enlarged, sincethe area of the individual photodiode 21 is small, the distance betweenthe center of each photodiode 21 and the transfer transistor 22 may beshortened. Therefore, since it is possible to improve charge transferefficiency, it is possible to suppress the occurrence of the afterimage.

In addition, in the embodiment, the unit pixel P includes microlenses MLwhich focus light to the photodiodes 21. In the unit pixel P, aplurality of the microlenses ML are disposed corresponding to aplurality of the photodiodes 21. Therefore, the incident light H isfocused on the light-receiving plane of each of the photodiodes 21, sothat the light receiving amount may be increased. Accordingly, it ispossible to improve sensitivity.

In addition, in the embodiment, a plurality of the floating diffusionsFD are disposed in the unit pixel P, and the plurality of the floatingdiffusions FD are electrically connected to each other by wire lines.Therefore, the efficiency of conversion of signal charges to a voltagein the floating diffusions FD may be decreased by adjusting FD wire linecapacitance, so that it is possible to appropriately perform signaldetection.

In general, the saturated signal amount of the solid-state imagingdevice is determined according to the number of the signal charges (thenumber of electrons or the number of holes) accumulated in thephotodiode 21, a range of the floating diffusion FD, and a range of thelatter-stage circuit (for example, an A/D converter).

Although the number of signal charges which may be accumulated in thephotodiodes 21 is increased by increasing the size of the unit pixel, Inthe case of exceeding the range of the floating diffusion FD, signaldetection is difficult. However, the signal detection may be performedby decreasing the conversion efficiency. In addition, since the numberof the signal charges which may be accumulated in the photodiodes 21 maybe increased, it is possible to prevent deterioration in image qualitycaused by light-shot noise.

Although the power consumption is increased in the case of increasingthe range of the floating diffusion FD or the range of A/D converter byincreasing the power supply voltage, it is unnecessary to increase thepower supply voltage according to the aforementioned configuration, sothat it is possible to reduce power consumption. In a small-sizedelectronic apparatus such as a capsule endoscope, no battery is providedtherein, or a battery having a small capacity is provided, so that verylow power consumption is necessary. Therefore, the aforementionedconfiguration is particularly suitable. In addition, since the thicknessof the gate oxide film is necessarily increased according to an increasein the power supply voltage, the occurrence of noise may be increased.Therefore, it is unnecessary to increase the power supply voltageaccording to the aforementioned configuration, so that it is possible todecrease the occurrence of noise.

Therefore, in the embodiment, it is possible to improve characteristicssuch as image quality of the captured color image.

In addition, in the aforementioned embodiment, although the case whereone amplification transistor 23 is disposed in the unit pixel P isdescribed, the invention is not limited thereto. The plurality of theamplification transistors 23 may be disposed in the unit pixel P.

2. Second Embodiment (A) Configuration and the Like of Apparatus

FIG. 13 is a diagram illustrating main components of a solid-stateimaging device according to a second embodiment of the invention.

In addition, FIG. 13 illustrates a cross section of one unit pixel Psimilarly to FIG. 6. In other words, in FIG. 13, a cross section of aportion taken along line XIII-XIII of FIG. 4 is illustrated.

As illustrated in FIG. 13, in the embodiment, an optical waveguide 131is disposed. Except for this point and the associated points, theembodiment is the same as the first embodiment. Therefore, with respectto the redundant portions, some description is omitted.

As illustrated in FIG. 13, the optical waveguide 131 is disposed at theside of the surface of the semiconductor substrate 101, on which theincident light H is incident.

As illustrated in FIG. 13, the optical waveguide 131 is formed to beinterposed between the microlens ML and the light-receiving plane JS ofthe photodiode 21, so that the incident light H incident through themicrolens ML is guided to the light-receiving plane JS of the photodiode21.

More specifically, the optical waveguide 131 is a core portion ofguiding light and is formed with an optical material of which thereflective index is higher than that of an insulating layer constitutinga wire-line layer 111 in the periphery thereof. For example, the opticalwaveguide 131 which is the core portion is formed so as to totallyreflect the incident light on the interface with respect to the cladportion.

(B) Conclusion

In this manner, in the embodiment, each unit pixel P includes theoptical waveguide 131 which guides light to the photodiode 21. Aplurality of the optical waveguides are disposed corresponding to thephotodiodes 21 disposed in each of the imaging portions (PA1, PA2, andthe like).

Therefore, the incident light H is guided to the light-receiving planesJS of the photodiodes 21 by the optical waveguides 131 with highefficiency, so that it is possible to increase the light receivingamount. Therefore, it is possible to improve sensitivity.

Therefore, in the embodiment, it is possible to further improve an imagequality of a captured color image.

3. Third Embodiment (A) Configuration and the Like of Apparatus

FIGS. 14 to 16 are diagrams illustrating main components of asolid-state imaging device according to a third embodiment of theinvention.

Herein, FIG. 14 illustrates an upper surface of an imaging area PA wherea plurality of unit pixels P are arrayed in a solid-state imaging devicesimilarly to FIG. 3.

In addition, FIG. 15 illustrates an upper surface of one unit pixel Psimilarly to FIG. 4. In other words, in FIG. 15, an upper surface of theunit pixel P (red pixel) where the red filter layer CFR in FIG. 14 isdisposed is exemplarily illustrated. In addition, the unit pixel P(green pixel) where the green filter layer CFG in FIG. 14 is disposedand the unit pixel P (blue pixel) where the blue filter layer CFB isdisposed also have the same configuration as the unit pixel P (redpixel) where the red filter layer CFR is disposed.

In addition, FIG. 16 illustrates a circuit configuration of one unitpixel P similarly to FIG. 5. In FIG. 16, similarly to FIG. 15, a circuitconfiguration of the unit pixel P (red pixel) where the red filter layerCFR in FIG. 14 is disposed is exemplarily illustrated. In addition, thegreen pixel and the blue pixel also have the same circuit configurationas that of the red pixel.

As illustrated in FIGS. 14 to 16, in the embodiment, the number of theimaging portions PA1 to PA4, PB1 to PB4, PC1 to PC4, and PD1 to PD4constituting the unit pixel P is different from that of the firstembodiment. Besides, the configuration of the unit pixel P is different.Except for this point and the associated points, the embodiment is thesame as the first embodiment. Therefore, with respect to the redundantportions, some description is omitted.

(A-1) Array of Unit Pixels

As illustrated in FIG. 14, similarly to the first embodiment, in thesolid-state imaging device, a color filter CF is disposed in each of theunit pixels P. The color filter CF includes a red filter layer CFR, agreen filter layer CFG, and a blue filter layer CFB and is disposed in aBayer array in each of the unit pixels P.

As illustrated in FIG. 14, each of the unit pixels P is configured toinclude a plurality of the imaging portions PA1 to PA4, PB1 to PB4, PC1to PC4, and PD1 to PD4. In the embodiment, a total of 16 imagingportions PA1 to PA4, PB1 to PB4, PC1 to PC4, and PD1 to PD4 are includedin the unit pixel P.

(A-2) Each Unit Pixel

As illustrated in FIGS. 15 and 16, in the unit pixel P, the imagingportions PA1 to PA4, PB1 to PB4, PC1 to PC4, and PD1 to PD4 are arrayedin the imaging plane (xy plane) so as to be aligned in units of four ineach of the horizontal direction x and the vertical direction y.

In the unit pixel P, two imaging portions are aligned in each of thehorizontal direction x and the vertical direction y, so that the groupsGA1, GA2, GB1, and GB2 including a total of the four imaging portions(PA1, PA2, PB1, PB2, or the like) are repetitively arrayed in thehorizontal direction x and the vertical direction y.

As illustrated in FIGS. 15 and 16, similarly to the first embodiment,among the groups GA1, GA2, GB1, and GB2, in each of the imaging portionsPA1 to PA4, PB1 to PB4, PC1 to PC4, and PD1 to PD4, a photodiode 21 anda transfer transistor 22 are disposed. In addition, in each of thegroups GA1, GA2, GB1, and GB2, under the set constructed with the fourimaging portions (PA1, PA2, PB1, PB2, and the like), a transistor groupconstructed as a set of an amplification transistor 23, a resettransistor 25, and a selection transistor 24 is disposed. In otherwords, the unit pixel P is disposed to include the four groups GA1, GA2,GB1, and GB2 which share the transistor group constructed as a set ofthe four imaging portions (PA1, PA2, PB1, and PB2).

However, as illustrated in FIG. 15, in the unit pixel P, a portion ofthe groups GA1, GA2, GB1, and GB2 including the four imaging portions(PA1, PA2, PB1, PB2, and the like) is configured to be different fromthe unit pixel P according to the first embodiment (refer to FIG. 4).

More specifically, in each of the groups GA1, GA2, GB1, and GB2, theposition of the floating diffusion FD is different from that in the unitpixel P according to the first embodiment. In addition, the positions ofthe transfer gates 22G are different. Except for this point and theassociated points, each of the groups GA1, GA2, GB1, and GB2 accordingthe embodiment is the same as the unit pixel P according to the firstembodiment.

As illustrated in FIG. 15, in each of the groups GA1, GA2, GB1, and GB2,a plurality of the floating diffusions FD are not disposed, but onefloating diffusion FD is disposed. The one floating diffusions FD aredisposed to be located between all the four photodiodes 21 disposed inthe imaging portions (PA1, PA2, PB1, PB2, and the like). In other words,the floating diffusions FD are disposed between the plurality of theimaging portions (a set of PA1 and PB2, a set of PA2 and PB1, or thelike) aligned in the vertical direction y, the horizontal direction x,and the direction slanted with respect to the vertical direction y andthe horizontal direction x.

As illustrated in FIG. 15, a plurality of the transfer gates 22G aredisposed in each of the groups GA1, GA2, GB1, and GB2. The transfergates 22G are disposed so that the floating diffusions FD are interposedbetween the four transfer gates 22G disposed in the imaging portions(PA1, PA2, PB1, PB2, and the like). In other words, the transfer gates22G are disposed so as to be aligned through the floating diffusions FDbetween the plurality of the imaging portions (a set of PA1 and PB2, aset of PA2 and PB1, or the like) aligned in the vertical direction y,the horizontal direction x, and the direction slanted with respect tothe vertical direction y and the horizontal direction x.

As illustrated in FIG. 16, in the unit pixel P, the groups GA1, GA2,GB1, and GB2 including the four imaging portions (PA1, PA2, PB1, PB2,and the like) are electrically connected to each other and are disposedso as to add the signals from the imaging portions and to output theadded signal.

More specifically, as illustrated in FIG. 16, in the unit pixel P, aplurality of vertical signal lines 27 are disposed, and each of thevertical signal lines 27 electrically connects the groups (a set OF GA1and GA2 or a set of GB1 and GB2) aligned in the vertical direction y.

In addition, the groups (a set of GA1 and GB1 or a set of GA2 and GB2)aligned in the horizontal direction x are electrically connected to eachother by the wire lines H34 and H13. Herein, in each of the groups GA1,GA2, GB1, and GB2, the wire lines H34 and H13 are disposed so as toelectrically connect wire lines which electrically connect the floatingdiffusions FD and the gate of the amplification transistor 23.

In addition, furthermore, a wire line HV is disposed so that the twovertical signal lines 27 are electrically connected to each other at theoutput end portions of outputting the electrical signal from the unitpixel P.

In the embodiment, the signal charges generated by the plurality of theimaging portions PA1 to PA4, PB1 to PB4, PC1 to PC4, and PD1 to PD4constituting the unit pixel P are added to be output as an output signalto each of the vertical signal lines 27. After that, the signal outputfrom each of the vertical signal lines 27 is smoothed by a smoothingcircuit (not shown) of the following stage.

(B) Conclusion

In this manner, similarly to the first embodiment, in the embodiment, inthe unit pixel P, the portions where the photodiodes 21, the transfergates 22G, and the floating diffusions FD are disposed are symmetricwith respect to the horizontal direction x and the vertical direction yas axes. Therefore, similarly to the first embodiment, vignetting ratiosof each color light in the upper portion and the lower portion of theimaging area PA become the same, so that it is possible to prevent theoccurrence of the color shading. Besides, similarly to the firstembodiment, it is possible to effectively prevent the occurrence of theafterimage or the like.

In addition, in the embodiment, in the unit pixel P, a plurality of theamplification transistors 23 are disposed, and a plurality of thevertical signal lines 27 are disposed. In addition, in the unit pixel P,the plurality of the vertical signal lines 27 is electrically connectedto each other. Therefore, as described above, the signals output fromthe plurality of the vertical signal lines 27 are smoothed, so that itis possible to reduce random noise.

Therefore, in the embodiment, it is possible to improve an image qualityof a captured color image.

4. Fourth Embodiment (A) Configuration of Apparatus

FIG. 17 is a diagram illustrating main components of a solid-stateimaging device according to a fourth embodiment of the invention.

Herein, FIG. 17 illustrates a circuit configuration of one unit pixel Psimilarly to FIG. 16. In FIG. 17, similarly to FIG. 16, a circuitconfiguration of the unit pixel P (red pixel) where the red filter layerCFR in FIG. 14 is disposed is exemplarily illustrated. In addition, thegreen pixel and the blue pixel also have the same circuit configurationas the red pixel.

As illustrated in FIG. 17, in the embodiment, the vertical signal line27 constituting the unit pixel P is different from that of the thirdembodiment. Except for this point and the associated points, theembodiment is the same as the third embodiment. Therefore, with respectto the redundant portions, some description is omitted.

As illustrated in FIG. 17, the groups GA1, GA2, GB1, and GB2 includingthe four imaging portions (PA1, PA2, PB1, PB2, and the like) aredisposed so that the groups GA1, GA2, GB1, and GB2 are electricallyconnected to each other so as to add the signals from the imagingportions and to output the added signal.

More specifically, as illustrated in FIG. 17, in the unit pixel P, onevertical signal line 27 which output the electrical signal from the unitpixel P is disposed, and the four groups GA1, GA2, GB1, and GB2 areelectrically connected to the one vertical signal line 27. In otherwords, in the unit pixel P, a plurality of the amplification transistors23 are disposed in each of the groups GA1, GA2, GB1, and GB2, and thesources of the amplification transistors 23 are electrically connectedto a common vertical signal line 27.

Therefore, in the embodiment, the signal charges generated by theplurality of the imaging portions PA1 to PA4, PB1 to PB4, PC1 to PC4,and PD1 to PD4 constituting the unit pixel P are added to be output asan output signal to the common vertical signal line 27.

(B) Conclusion

In this manner, similarly to the third embodiment, in the embodiment, inthe unit pixel P, the portions where the photodiodes 21, the transfergates 22G, and the floating diffusions FD are disposed are symmetricwith respect to the horizontal direction x and the vertical direction yas axes. Therefore, similarly to the third embodiment, vignetting ratiosof each color light in the upper portion and the lower portion of theimaging area PA become the same, so that it is possible to prevent theoccurrence of the color shading. Besides, similarly to the firstembodiment, it is possible to effectively prevent the occurrence of theafterimage or the like.

In addition, in the embodiment, the plurality of the amplificationtransistors 23 are disposed in the unit pixel P, and the sources of theplurality of the amplification transistors 23 are electrically connectedto a common vertical signal line 27.

Therefore, in the embodiment, it is possible to improve the imagequality of the captured color image.

5. Others

When the invention is embodied, the invention is not limited to theaforementioned embodiments, but various modified examples may beemployed.

For example, in the aforementioned embodiments, although the case wherethe invention is adapted to a camera is described, the invention is notlimited thereto. The invention may be adapted to other electronicapparatuses having a solid-state imaging device such as scanners orcopiers.

In the aforementioned embodiments, although the case where four orsixteen photodiodes are disposed in the unit pixel P is described, theinvention is not limited thereto. An appropriate number of thephotodiodes may be disposed in the unit pixel P.

In addition, although the pixel transistor including four types oftransistors, that is, the transfer transistor, the amplificationtransistor, the selection transistor, and the reset transistor aredisclosed, the invention is not limited thereto.

In addition, in the aforementioned embodiment, the solid-state imagingdevice 1 corresponds to a solid-state imaging device according to theinvention. In addition, in the aforementioned embodiment, the unit pixelP corresponds to a unit pixel according to the invention. In addition,in the aforementioned embodiment, the imaging area PA corresponds to animaging area according to the invention. In addition, in theaforementioned embodiment, the photodiode 21 corresponds to aphotoelectric conversion portion according to the invention. Inaddition, in the aforementioned embodiment, the transfer gate 22Gcorresponds to a transfer gate according to the invention. In addition,in the aforementioned embodiment, the floating diffusion FD correspondsto a floating diffusion according to the invention. In addition, in theaforementioned embodiment, the amplification transistor 23 correspondsto an amplification transistor according to the invention. In addition,in the aforementioned embodiment, the vertical signal line 27corresponds to a vertical signal line according to the invention. Inaddition, in the aforementioned embodiment, the microlens ML correspondsto a microlens according to the invention. In addition, in theaforementioned embodiment, the optical waveguide 131 corresponds to anoptical waveguide according to the invention. In addition, in theaforementioned embodiment, the camera 40 corresponds to an electronicapparatus according to the invention.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2010-107265 filedin the Japan Patent Office on May 7, 2010, the entire contents of whichare hereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An imaging device comprising a semiconductorsubstrate and a plurality of unit pixels, wherein each of the unitpixels comprises: a first photoelectric conversion element; a secondphotoelectric conversion element; a first floating diffusion region; asecond floating diffusion region; a first transfer gate disposed betweenthe first photoelectric conversion element and the first floatingdiffusion; a second transfer gate disposed between the secondphotoelectric conversion element and the second floating diffusion; asignal line; an amplification transistor connected to output anelectrical signal to a column circuit via the signal line; and a wireline, wherein, the signal line extends along a first direction, thefirst floating diffusion region and second floating diffusion region arearranged along a second direction that is different from the firstdirection, the first floating diffusion region and the second floatingdiffusion region are formed in the semiconductor substrate, and a gateof the amplification transistor is electrically connected to the firstfloating diffusion region and the second floating diffusion region viathe wire line.
 2. The imaging device of claim 1, wherein each of theunit pixels further comprises: a third photoelectric conversion element;and a fourth photoelectric conversion element.
 3. The imaging device ofclaim 2, wherein each of the unit pixels further comprises: a thirdtransfer gate disposed between the third photoelectric conversionelement and the first floating diffusion region; and a fourth transfergate disposed between the fourth photoelectric conversion element andthe second floating diffusion region.